1. Field of the Invention
The present invention relates to a vehicle driveability evaluation system which is capable of evaluating an influence of a characteristic of a performance of an engine on the driveability of a vehicle on which the engine is to be installed, by operating the engine on a test bed without installing it on the vehicle body.
2. Description of the Related Art
Heretofore, an influence of a characteristic of an engine performance on a driveability of a vehicle (including the comfort of the vehicle as well as vehicle performance such as an acceleration, vibration, noise) was tested by actually driving a vehicle mounted with the actual engine on a test course or a public road. However, the test of the driveability on a test course or a public road requires considerable time and cost, and there has been a long-standing need for a vehicle driveability evaluating system which is capable of evaluating a driveability of a vehicle (i.e., a combination of a specific vehicle body and a specific engine) without actually driving the vehicle.
Japanese Unexamined Utility Model Publication (Kokai) No. 61-125740 discloses one type of the vehicle driveability evaluation system of this kind. The system in the '740 publication uses a chassis dynamometer to evaluate the vehicle driveability. In the system of the '740 publication, a complete vehicle including an actual vehicle body and an actual engine is tested, i.e., the complete vehicle is placed on a rotating drum of a chassis dynamometer, and the vehicle is driven under various running resistance given by the chassis dynamometer. The system in the '740 publication detects the rotational speed of the rotating drum (i.e., a running speed of the vehicle), and extracts low frequency components from the rate of change in the rotational speed of the drum (i.e., the differential value of the running speed of the vehicle). Further, the system indicates the magnitude of the low frequency components on an analog gauge or an LED indicator.
It is known that the magnitude of the low frequency components of the rate of change in the running speed has a relationship with the magnitude of a surge, i.e., a low frequency vibration of the vehicle body in the longitudinal direction, and the surge of the vehicle largely affects the driveability of the vehicle. Therefore, the system in the '740 publication is capable of acquiring a driveability data (the low frequency component of the change in the running speed of the vehicle) which represents the driveability of the vehicle (in this case, the magnitude of the surge) without actually driving the vehicle on the test course or a public road.
Although the system in the '740 publication is advantageous in that it allows evaluation of the magnitude of the surge without actually driving the vehicle on a test course or a public road and shortens the time required for the vehicle driveability evaluation test, the system in the '740 publication has some problems.
For example, the system in the '740 publication requires a complete vehicle for testing the driveability. Therefore the complete vehicle body and the engine must be available when the test is carried out. However, in some cases, it is preferable to evaluate the influence of the engine performance characteristic on the driveability of the vehicle before the vehicle body is manufactured so that the engine can be modified to improve the driveability of the vehicle. In such a case, the system in the '740 publication cannot be used.
Further, since the test vehicle is driven on the rotating drum of the chassis dynamometer in the system of the '740 publication, it is difficult to simulate various running condition (such as running conditions on a rough road, slope or highway) of the vehicle and the driveability of the vehicle cannot be tested in the various running conditions.
Further, the magnitude of the low frequency components of the rate of change in the vehicle running speed is indicated as a numerical value, or the magnitude of the low frequency components is roughly divided into ranges in accordance with the magnitude of the influence thereof on the driveability and the ranges are indicated by the LED indicator in the '740 publication. However, since it is difficult for an inspector to comprehend the influence on the driveability from the numerical value or the indication of the LED indicator, the influence on the driveability is not evaluated correctly in some cases. Especially, since the magnitude of the influence of the factors such as acceleration and vibration on the driveability cannot be quantified, it is difficult to evaluate the magnitudes of influences of these factors on the driveability even if these factors are expressed in numerical values.